(1) Field of the Invention
The present invention relates generally to drag and noise associated with a fluid flow and more particularly to a method and apparatus that reduces drag and noise associated with fluid flow in a conduit.
(2) Description of the Prior Art
Drag and noise reduction associated with a fluid flow in a conduit has always been a concern for a variety of reasons. Basically, drag between the fluid and internal conduit walls causes a pressure loss leading to increased power consumption. Similarly, the flow noise generated within the conduit may adversely affect the surroundings as well as the individuals working therein.
Accordingly, several prior art systems have been developed to reduce drag and/or flow noise. For example, long-chain polymer solutions have been injected into a fluid flow to reduce the fluid's viscosity (drag). However, this is not always practicable since the fluid being transported may need to be kept free from such contamination. Furthermore, the performance of such a polymer solution is generally subject to degradation over time.
Another possible prior art drag reduction method involves the injection of microscopic air bubbles along the inside walls of the conduit thereby introducing a thin layer of air between the conduit walls and the fluid flow to reduce drag therebetween. However, the use of the "micro" bubbles has not proven to be an effective method of drag reduction as experimental results are not conclusive. Furthermore, neither the polymer solution injection nor the micro bubble injection (drag reduction) approach is concerned with the simultaneous reduction of flow noise.
One prior art method that does attempt to reduce drag and flow noise simultaneously is known as flow path streamlining. However, because this often involves redesigning and modifying the entire conduit system, it can be costly and difficult to implement. Traditionally, flow noise reduction has been accomplished by lining the inside wall of the conduit with sound absorbent materials or, alternatively, reducing the velocity of the fluid flow. However, use of absorbent materials may be limited by space constraints in certain system configurations while reduction in flow velocity is not a desirable tradeoff.